Apparatus and process for subdividing sealed glass tube containing radioactive gas

ABSTRACT

A sealed glass tube containing a luminophor and a radioactive gas is subdivided by heating the tube to fusion by means of a laser beam. The tube is heated within a sealed enclosure and means are provided for regulating the pressure within the enclosure so that the pressure exceeds that within the glass tube.

June 18, 1974 o. THULEF? 7 3,817,733 APPARATUS AND PROCESS EORSUBDIVIDING SEALED GLASS TUBE HCDJITAINING RADIOAGTIVE GAS Filed May 16,I972 United StatesPatent O US. Cl. 65-56 3 Claims ABSTRACT OF THEDISCLOSURE A sealed glass tube containinga luminophor and a radioactivegas is subdivided by heating the tube to fusion by means of a laserbeam. The tube is heated within a sealed enclosure and means areprovided for regulating the pressure within the enclosure so that thepressure exceeds that within the glass tube.

CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of my cop'ending application Sen-No. 832,273 filedJune 11, 1969, now Pat. No. 3,706,543, granted Dec. 10, 1972.

BACKGROUND OF THE INVENTION A process for the subdivision of a long,sealed glass tube containing a luminophor and a radioactive gas wherethe subdivision is carried out by heating a zone of the glass tube tofusion and wherein the pressure within the glass tube is sub-atmospherichas been disclosed in my copending Pat. No. 3,706,543. The use of thelaser beam represented a substantial .improvement over the prior art inthat the tube was heated to the temperature of fusion so rapidly thatheat transfer along the tube was minimized, thereby minimizing damage tothe luminophor in adjacent portions of the tube.

The method of subdivision described in the aforenoted application sharedthe limitation common to .all processes of production radioactive lightsources: to a make a gastight seal, the internal gas pressure must bebelow atmospheric pressure. Otherwise, when the glass becomes soft underthe influence f the flame or the laser beam, the softened glass forms aballoon which may burst and release radioactive gas instead ofcollapsing so that whenthe divided-off tube is pulled away from the longtubular source, a gas-tight seal is formed on both sides. Moreover, thegas pressure within the tube must not be so far below atmospheric thatthe collapsed glass is sucked inwardly to form a fragile seal. As isevident, the internal and external pressures must be so related thata'proper gas-tight seal is formed on both of the ends produced in theprocess. However, the lower the gas pressure within the final lightsource, the lower the brightness of the source produced. The higher gaspressure always yields a higher brightness.

A number of different methods have been attempted as a means ofby-passing the limitation that the gas pressure within the source mustbe below atmospheric. For instance, the source to be sealed oil? iscooled as by immersion in liquid nitrogen. Such cooling drops theinternal pressure by an amount which is approximately proportional tothe drop in absolute temperature. The conditions to make a gas-tightseal are then met, the pressure and 1 therefore the brightness will becorrespondingly higher as compared with a source which is sealed offwithout immersion in a cooling medium. By using liquid nitrogen as thecooling medium, where the liquid nitrogen has a ice temperature of aboutK., a source having'a pressure about 3.3 times greater than wouldotherwise be the This process by means of which it is possible toprovidesources with higher internal pressure and brightness has beenused with some success. However, it is tedious, but more important, theportion which is cooled and which is to be subdivided off from the mainportion will containa quantity of gas such that when sealed off andreturned to room temperature, the pressure within the sealed off portionwill be about 3 times as high as the pressure in the original long tube.However, as successive portions of the long tubexare sealed off andremoved, the pressure of the remaining gas in the long tube will' becomedepleted so that the final sources manufactured in this way may havepressures which are even lower than atmospheric. Consequently, theprocess suffers from the-major disadvantage that light sourcesmanufactured in this way will vary very substantially in the brightnessthereof. This technique, therefore, is used only when the source to becut off can be maintained in contact with a large reservoir ofradioactive gas which can either be replenished or where the depletion.effect is negligible.

SUMMARY OF THE INVENTION Radioactive light sources containing aluminophor and a radioactive gas at super-atmospheric pressure where thelight sources are essentially equal in brightness can be manufactured bysubdividing a long tube containing a luminophor and a radioactive gaswhile the tube is encased in a sealed chamber, the pressure of which canberegulated ,so that it is higher than that within the sealed tube by asuitable amount. The pressure within the sealed chamber is-so regulatedthat on heating the sealed tubewith a laser beam, the sealed tubecollapses quickly so that a portion of the sealed tube may be withdrawnfrom the remainder, both the'withdrawn portion and the sealed tubehaving new ends formed thereon, the ends being strong and hermetic.

The use of a sealed chamber for the operation constitutes a protectionagainst the possibility of exposure to radioactive gas followingaccidental breakage of the radio.- active gas-containing tube.

Accordingly, an object of the present invention isv to provide improvedradioactive light-sources having in creased luminosity. I

Another object of the present invention is to provide improvedradioactive light-sources having'strong, hermetic end seals.

- A further object of the present invention is to provide an improved.process for producing radioactive light! sources wherein the process ofsubdividing a long tube containing a luminophor and a radioactive gas iscarried out within a sealed chamber.

Still another object of the present invention is to pro-- vide animproved process for producing radioactive lightsourccs wherein theprocess is carried out within a sealed chamber, and the dillercuce inpressure between that in the radioactive light-source and that in thesealed chambcr can be controlled.

Still another object of the present invention is to provide an improvedprocess for manufacturing radioactive light-sources wherein the processis carried out within a; sealed chamber and a laser beam is used for theheating of the sealed tube.

Still other object and advantages of the invention will in part beobvious and will in part be apparent from the specification. v

The invention accordingly comprises the several steps and the relationof one or more of such steps with respect 3 to each of the others, andthe-apparatus embodying features of construction, combination ofelements and arrangement of parts which are adapted to effectsuch-steps, all as exemplified in the following detailed disclosure, andthe scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawing, in which:

The single Figure shows diagrammatically the apparatus of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A long tubular light source 1 isproduced by sealing it the glass tube can withstand is introduced intothe.ap-

. paratus in the interior of pressure chamber 14 through off whenimmersed in a cooling medium such as liquid nitrogen and when in contactwith a large reservoir of radioactive gas. This step, of course, isconventional. To carry out the steps of subdividing this long tube inaccordance with the present invention, the tube 1 is placed in agas-tight enclosure 14, this enclosure containing a suitable gas such asnitrogen at a pressure higher than that of the radioactive gas in theinterior of long tubular light source 1. i

As shown diagrammatically, laser 6 produces output beam 7 in a directionwhich is preferably perpendicular to the glass tube'l. A focusing device8 for controlling the Output beam 7 where the focusing device is a Kerrcell or crossed prism sets up a parallel beam 9 which is directed towardthe glass tube 1 at the point to be fused. Preferably, the laser beam 9at that stage has about the same cross section in the glass tube,- thusproviding that enough glass will be fused to form strong, hermetic sealsas tube 1 is subdivided.-

A metal plate 10 is fitted beside laser beam 9. The metal plate 10 canbe swung in and out of position to stop the beam 9 from reaching tube 1when so desired.

A metal reflector 11 may be provided on the further side of tube ,1 toreflect any laser beam portion which passes tube 1 thereby preventingloss of energy and increasing the rate at which the heated zone of tube1 is brought to the fusion temperature.

Laser beam 7 preferably has a wave length range lying within the optimumabsorption range of the glass of which tube 1 is made. Laser 6 can, forinstance, be of the CO type-which can produce a beam with a wave lengthof 10.6 microns at an output wattage ofabout 100 watts.

Chucks '2 and 5 are provided for holding the main portion of tube 1 andthe-portion which is to be cut off respectively. Both chucks 2 and 5 canbe rotated in unison by means not shown andchuck 5 can be used toseparate off the portion of light source 1 by moving the portion in thedirection 13 after fusion and sealing are complete.

. Laser beam 9 enters sealed chamber 14 through a suitable window 22which is transparent to the laser light. Window 22 is preferably ofpotassium chloride.

Space 15 in sealed chamber 14 can be brought to any absolute. pressurefrom zero to as high as desired by means of pump or gassupply 16, andregulator 17 which is provided with a compound gauge 23, The upperpressure limit must, of course, be somewhat higher than that in anyglass tube which is to be sealed. Connection between regular 17 andspace 15 is made by means of tube 18.

Control unit 19 is indicated diagrar'nmatically; this control ,unitsupplies electrical signals into the interior of enclosure 14controlling devices (not shown) which carry out the mechanical movementsnecessary for sealing off short portions from the main portion of longtubular source 1.

The procedure is the following:

A longtubular source 1 containing radioactive gas at any pressure abovezero and up to the maximum which L gas-tight door" 21 In general themaximum gas pressure is about 9 atmospheres absolute. The apparatusholdsthe long tubular light source by means of the chucks 2 and 5 whichrotate source 1 in unison. Door 21 is then closed and the pressurewithin the chamber 14 is brought to the desired level. This pressure isso chosen that when a short' section is sealed off from the long tube 1by means of laser beam 9, the pressure difference between the inside ofthe source and the interior of enclosure 14 will cause tube'l tocollapse at the zone heated by laser beam 9, forming a hermetic-seal.Drawing sealed-off portion to the left by means of chuck 5 results inthe formation of properly shaped convex end seals. As successivesections are removed from source 1 the pressure on theinside.

thereof will-change somewhat. The operator of the apparatus can observethe way in which the tube 1 collapses as .it is heated and can adjustthe pressure within the enclosure 14 by means of regulator 17 to ensurethateach seal produced is properly convex and hermetic.

I When a source has'been completely subdivided into smaller sources,atmospheric pressure is established by opening valve 20 which leads toan exhaust system (not shown). Door 21 is then opened, a new tubularsource to be subidivided -is introduced through it into the apparatusand the procedure is repeated. The light sources which are sectionedfrom the tube 1 are removed through a door (not shown) at the bottom ofsealed chamber 14.

Where it is desired to operate at sub-atmospheric pres- I sure, a vacuumpump (not shown) can be attached to valve 20, thus providing foroperation of sealed chamber outside sealed chamber 14 by the use ofmagnetic forces.

Also, the operation of pressure regulator 17 to alter the pressurewithin enclosure 14 could be made controllable by a device which sensesthe form of the end seals being produced at the separated ends of tube1.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may bemade in carrying out the above process andin the construction set forth without departing from the spirit andscope of the invention,-it is intended that all matter contained in theabove description and shown in the accompanying drawings shall beinterpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of f long sealed glasstube is to be divided, so that a sufficient quantity of glass is drawnin from the side wall to form end walls, wherein the improvementcomprises a. scalable chamber in which said heating of said long, glass.sealed tube at said zone can be carried out and in which the pressurecan be adjusted to exceed that within said sealed tube by a controlleddifference, first and second chucks for holding said glass tube oneither side of said zone, said first chuck holding that portion of glassto be divided off, said chucks being rotatable in unison at least duringthe period of heating said zone to fusion, and so mounted in saidchamber that after heating said zone to fusion said first chuck ismovable away from said zone and operable to release said shorter sealedtube and then returnable to its original position to receive, hold androtate a s us'b fusion by said laser beam to form a short sealed tubeand quent portion of said remainder to be divided off, said second chuckbeing movable toward said heating zone, after dividing off a portionthereof, to feed a subsequent por-' ,tion of said-sealed glass tube intosaid first chuck to be grasped and rotated thereby, said difference inpressure being such as to ensure that the zone which is heated collapsesto form strong, hermetic seals at the ends of said divided-off shortertube and of said remainder, means for decreasing the pressure in saidchamber to a selected level below atmospheric pressure and means forraising the pressure in said chamber above atmospheric pressure,

both of said means being operatively connected to said chamber.

2. An improved process for dividing a long, sealed glass tube containinga luminophor and a radioactive gas into a shorter sealed tube and aremainder without loss of radioactive gas wherein said long, sealed,glass tube is heated to fusion by a closely localized laser beam over anarea such that a sufiicient quantity of glass may be drawn in from theside wall to form end walls and simultaneously seal the ends of theshorter tube and the remainder, the improvement comprising the steps ofintroducing said long tube into a scalable pressurizable chamber fittedwith a window through which said laser beam may be introduced to heatsaid tube at a closely localized zone and with first and second chuckstherein, said chucks being mounted for rotation in unison about a commonaxis and for movement in both axial directions, said chucks beingpositioned on either side of said heating zone, introducing said sealedtube to be divided into shorter segments into both of said chucks,sealing said chamber, adjusting the pressure in said chamber eitherupwardly or downwardly as needed to establish a selected pressuredifference above that in heated to fusion, collapses to form strong,hermetic seals at the ends of said divided-01f shorter tube and of saidremainder.

3. The process as defined in claim 2 wherein the pres sure 'in said'sealed chamber is adjusted periodically during the division of a longtube to compensate for changes in pressure within said tube. as eachsegment is divided ott'.

References Cited UNITED STATES PATENTS 3,265,855 8/1966 Norton --112 X3,434,818 3/1969 Chauvin 65-270 X 3,453.097 7/1969 Hilfner 651l2 X3,505,050 4/1970 Huston 65-270 X 3,706,543 12/1972 Thuler 65112 X3,318,512 5/1967 Linlor 65-412 X ROBERT L. LINDSAY, 111., PrimaryExaminer U.S. Cl. X.R. 65--1 05, 153, 273

